Effects of acid treatment on electrochemical properties of Li2MnO3·LiNi0.5Co0.45Fe0.05O2 cathode materials

Abstract

A new composite, Li2MnO3·LiNi0.5Co0.45Fe0.05O2, can be synthesized by a solid-state method and preconditioned with 5 wt% HCl, H2SO4, or H3PO4 solution to achieve H+/Li+ exchange. The effects of acid treatment on the structure, morphology, and electrochemical properties of Li2MnO3·LiNi0.5Co0.45Fe0.05O2 cathode materials are analyzed. The X-ray powder diffraction patterns imply that the hexagonal α-NaFeO2 structure (space group R $$\bar{3}$$ m) of the materials is not changed by the acid treatment. The scanning electron microscope images show that particles become spherical with smooth surfaces after acid treatment, and the Brunauer–Emmett–Teller analysis reveals that the specific surface area increases. The charge–discharge test demonstrates that acid-treated Li2MnO3·LiNi0.5Co0.45Fe0.05O2 cathode materials deliver higher initial coulombic efficiencies than untreated material, owing to the improvement of the catalytic reduction activity of oxygen released during the initial charge process. Furthermore, Li2MnO3·LiNi0.5Co0.45Fe0.05O2 treated with HCl displays the best electrochemical performance, with the acid treatment improving the initial coulombic efficiency from 66.0 to 82.2%. Thus, acid treatment can effectively improve the electrochemical performance of electrode materials in Li-ion batteries.